1. Field of the Invention
This invention relates to a grain cleaning apparatus and, more specifically, this invention relates to a grain cleaning apparatus having an integral proportional bypass for diverting a portion of incoming grain flow from a screening area directly to a grain outlet.
2. General Description of the Prior Art
In grain handling operations, it is often necessary to reduce the amount of relatively small foreign material, such as dust, seeds, chaff, etc., mixed with grain before storage or shipment thereof. For example, removal of foreign material from grain can increase the efficiency of grain dryers because moisture is typically preferentially absorbed by foreign material. Further, grain cleaning is desirable before storage because small foreign material tends to accumulate near the center of stored grain, thereby obstructing air flow from aeration systems which protect the grain from heating and deterioration.
The Federal Inspection Grain Service Division of the U.S. Department of Agriculture has promulgated regulations requiring that certain grades of corn, soybeans, wheat and other grains may contain, when shipped, no more than specific maximum levels of foreign material. Any shipment of grain containing foreign material in excess of its market grade tolerance is "docked" according to a published scale and results in a net loss of income to the shipper.
It is not desirable to reduce the level of foreign material in shipped grain below the maximum level allowed by federal regulations, for economic reasons. Therefore, it is desirable to control the percentage of foreign material removed from grain before shipment.
One form of grain cleaner which has achieved widespread acceptance utilizes gravity flow of grain over a series of screens within an upstanding housing. Grain flows through an inlet at the housing's upper end and is directed outwardly and downwardly over a first layer of screens. Relatively small particles of foreign material fall through the screens into a first foreign material chamber communicating with a foreign material outlet at the housing's lower end.
Grain reaching the outer periphery of the first level of screens reverses its direction of flow and is directed downwardly and inwardly over a second layer of screens overlying a second foreign material receiving chamber, also communicating with the foreign material outlet. Relatively clean grain is received at the bottom of the second level of screens and is directed to a clean grain outlet chute which communicates with a storage facility, vehicle or other grain receiving means.
Such a grain cleaner is typically an integral part of a continuous grain handling system, and may be disposed between a dry elevator leg and a grain storage tank, or between a wet elevator leg and a grain dryer, for example. If relatively clean grain, not requiring cleaning, is to be transferred through a system having a grain cleaner, it may be desirable to bypass the cleaner's screens by means of external lines or integral bypass means.
One such well-known integral bypass system used with grain cleaners of the type described above comprises a grain-receiving valve box disposed below the grain inlet and generally at the upper screen level and having a selectively open or closed gate at its lower end. When the gate is closed, grain flowing into the box fills and overflows the box to the upper screen layer. When the gate is open, all grain entering the grain inlet is directed downwardly through the box and through the first foreign material receiving chamber and to the grain outlet through a second gate disposed at the bottom of the first foreign material receiving chamber. When the valve box gate is closed, the lower gate is positioned to place the foreign material outlet in communication with the foreign material receiving chamber to prevent contamination of clean grain with foreign material and to allow removal of foreign material through the foreign material outlet. Due to the relationship between the positions of the upper and lower gates, it is impossible to proportion the flow of incoming grain between the screens and the foreign material chamber; only "on-off" bypass operation is possible.
Control of the foreign material content of discharged grain is relatively difficult with a grain cleaner having the integral bypass means described above due to the lack of a proportional cleaning capability. Lack of control of foreign material content results in diseconomies or in undesirable excessive foreign material levels in shipped grain.